1. Field of the Invention
The present invention relates to an apparatus and a method for reducing cross-talk between audio channels of a mobile terminal. More particularly, the present invention relates to an apparatus and a method for reducing cross-talk between left audio channel and right audio channel of a mobile terminal equipped with an earphone antenna.
2. Description of the Related Art
Recently, a mobile terminal that supports an earphone antenna, that is, an earphone having a Frequency Modulation (FM) radio antenna function has been developed.
Generally, EAR_COM of a mobile terminal serves as a reference potential with respect to left audio channel and right audio channel of an earphone and must be connected to a ground (GND) of a system. However, since EAR_COM uses the same signal line as a line for an FM radio antenna signal due to limitation in the number of input/output (I/O) port inside the mobile terminal that supports the earphone antenna, EAR_COM is connected to GND via an inductor.
FIG. 1 is a circuit diagram illustrating a mobile terminal that supports an earphone antenna according to the conventional art. As shown in FIG. 1, since the mobile terminal that supports the earphone antenna commonly uses an EAR_COM port and an FM radio antenna (FM_RADIO_ANT) port, EAR_COM is not directly connected to GND 101 but is connected via an inductor 103. Here, ideally, the inductor 103 has resistance of 0 for a Direct Current (DC) and has increasing resistance for an Alternating Current (AC). Accordingly, when the inductor 103 is applied in parallel as illustrated in FIG. 1, a DC-like potential maintains the same potential as GND 101, and an FM radio signal having a frequency ranging from 80 MHz to 110 MHz does not go to GND 101 but is transferred up to an FM signal tuner 105.
However, since the inductor 103 has DC resistance, a mutual interference phenomenon, that is cross-talk between left audio channel and right audio channel is generated which in turn deteriorates stereo performance. FIG. 2 is a view illustrating a case where cross-talk is generated in an earphone antenna connected to the conventional mobile terminal. As illustrated in FIG. 2, a current of an audio signal is input to a (+) port of a left channel (EAR L) 201, passes through a (−) port, and goes to EAR_COM to move a vibrating plate of the earphone. At this point, a current of the audio signal cannot swiftly fall due to the DC resistance component 205 of the inductor connected to EAR_COM, so that a portion of the signal is directed to a right channel (EAR R) 203 causing cross-talk.
As described above, to remove cross-talk between left audio channel and right audio channel of the earphone, an inductor having low DC resistance needs to be used. However, for performance of FM radio reception sensitivity, an inductor having high DC resistance is required.